It’s just around the corner… but what is Amazon Prime Day?

Amazon.com wants you to get primed for its third annual Prime Day, a sort of "Christmas in July" with 30 hours of deals for the online shopping giant kicking off Monday night at 9 p.m. EST. But make sure you buy smart before you get crazy with that shopping cart.

"Prime Day is really just a giant marketing day for Amazon," Business Insider's Lauren Lyons Cole told NBC News. "They're going to sell a ton of products and they're also going to get a ton of new Prime subscribers."

For starters, you'll need to be a member of Amazon Prime, its $99/year member subscription program, in order to participate. If you buy at least 15-20 items per year on Amazon, it's likely worth it just for the free two-day shipping. Amazon does also offer free, 30-day trials of Amazon Prime.

Throughout the day there will be two types of deals. Some are all-day and some are "Lightning" deals, which end after a fixed time or when stock runs out. For better deals or those with limited inventory, that can be within a matter of minutes. New deals will be released every five minutes on everything from toys to toasters to televisions, including 50 percent off Amazon Echo for $89.99, a 55-inch 4K HD TV for $399.99, and up to 40 percent off Radio Flyer, Crayola, and K'NEK kids items.

Deal-seekers should also consider downloading the Amazon app, which will give a roster of upcoming deals 24 hours in advance. That way you can schedule time to go shopping for the categories you're interested in instead of just sitting in front of your computer and clicking refresh.

But remember to shop smart and not get caught up in the Candy Crush-like frenzy of getting a deal for getting a deal's sake. According to top gadget review site The Wirecutter, less than 1 percent of the 8,000 Amazon Prime Day deals they analyzed last year qualified as "great" deals.